Variable displacement engine (VDE) designs are well known in the art for providing increased fuel efficiency by deactivating cylinders during operation modes requiring decreased engine output. Such designs may also incorporate cam profile switching (CPS) to enable high or low lift valve train modes which correspond to increased fuel efficiency during high and low engine speeds, respectively.
In CPS systems, a VDE design may be supported through a no-lift cam profile that deactivates cylinders based on engine output needs. As an example, U.S. Pat. No. 6,832,583 describes an engine valve train having multiple valve lift modes including cylinder deactivation. The described example utilizes high and low lift cams on the valve train which can be further modified so that low lift corresponds to a zero-lift deactivation setting.
However, the inventors herein have recognized that such an approach does not incorporate three distinct lift profiles for one cylinder. Generally speaking, mechanisms for deactivating valves or enabling a third lift profile require more space along the length of an overhead camshaft. The placement of cam towers and cylinder bore spacing requirements further inhibit the inclusion of multiple valve lift profiles and/or cylinder deactivation mechanisms.
In order to address these issues, systems and methods for an overhead cam shaft coupled to an inline engine with inner cylinders and outer cylinders are provided. In one example approach, an engine bank comprises inner cylinders each having only first and second lift profiles, both being non-zero lift profiles, and outer cylinders each having first, second, and third lift profiles, two being non-zero lift profiles and one being zero lift.
In this way, an engine cylinder head design in which a third, zero-lift profile may be included in some cylinders having both first and second lift profiles. For example, a cylinder head may be enabled with a camshaft having high and low lift cam profiles on all cylinders, and selective deactivation of outer cylinders only by inclusion of a third, zero-life profile on these cylinders. Such an approach utilizes additional space located on the outer camshaft as per some pre-existing engine cylinder head designs and asymmetrical cam tower placement to allow sufficient space for the different cam profiles over both outer and inner cylinders without intruding on inner cylinder spacing. Such an approach has the potential advantage of enabling VDE and CPS concurrently in a more compact engine design such as an inline, four-cylinder engine. Further, such an approach may enable flexibility of using the same engine architecture on multiple vehicle platforms.
While one example shows two lift profiles on inner cylinders and three lift profiles on outer cylinders, the present application recognizes that in another example, outer cylinders may have fewer discrete lift profiles than inner cylinders, where inner cylinders have wider cam tower placement as compared to outer cylinders.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.